#11709: FareySymbol
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Reporter: hmonien | Owner: craigcitro
Type: enhancement | Status: needs_review
Priority: major | Milestone: sage-5.0
Component: modular forms | Resolution:
Keywords: Farey symbol | Work_issues:
Upstream: N/A | Reviewer: Martin Raum, Leif Leonhardy,
David Loeffler
Author: Hartmut Monien | Merged:
Dependencies: |
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Comment(by davidloeffler):
Wait a minute, here's a bug.
{{{
sage: G = ArithmeticSubgroup_Permutation(S2="(1,2,3,4)",S3="(1,3)(2,4)")
sage: gens = FareySymbol(G).generators(); [x.matrix() for x in gens]
[
[1 2] [ 0 -1] [ 1 -1]
[0 1], [ 1 -1], [ 1 0]
]
sage: gens[0] in G
False
}}}
This has the disastrous consequence that {{{ G.is_congruence() }}} returns
False, even though G is actually congruence (of level 4).
For some reason, the mechanism that checks whether the potential generator
is actually in the group, and if not flips its sign, doesn't seem to be
working for this particular group G. It seems to work for all the other
ones I've tried though. Hartmut: any thoughts?
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/11709#comment:36>
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